This invention pertains generally to the field of electrolytic capacitors ("elcaps") and to the construction of such capacitors in order to improve their heat dissipating properties.
Generally, choosing appropriate materials for the manufacture of the capacitors or heat sinks, treatment methods for improving the efficiency of heat sinks, techniques for mountings capacitors or heat sinks to a chassis or frame, and the selection of appropriate insulation pads, etc. are known or readily determinable by those skilled in the art. Attention is directed to the appropriate texts and references known to those skilled in the art for details regarding these and other concepts. See e.g., Electrolytic Capacitors, by Paul McKnight Deeley (The Cornell-Dubilier Elec. Corp., S. Plainfield, N.J., 1938).
An electrolytic capacitor generates internal heat due to fluctuating current ("ripple current") during operation. This necessitates a design for the capacitor which will conduct heat from the core of the capacitor to the outside environment. For cylindrical elcaps, radial and axial heat flow serves to conduct the heat from the core of the capacitor to the sides and bottom of the package in which the capacitor is encased. Dissipation of the heat from the package of the capacitor to the outside environment is limited by the external thermal resistance between the package and the ambient air.
If the package (or "can") surface area is made larger without impeding heat flows from the roll to the can, then the capacitor dissipates more heat and thus handles more ripple current. Capacitors should be made in as small a can as possible to achieve more efficient heat flow from the roll to the can. Low height to diameter ratios are desirable, where feasible, to take advantage of high axial heat flow. However, low height seriously degrades surface area to volume ratio, thus raising thermal resistances.
Other techniques for conducting heat from the core of an electrolytic capacitor to its package with improved efficiency are known. For instance, U.S. Pat. No. 4,546,415 describes features for conducting heat from the core of the capacitor to the package. Capacitors so constructed would appear to have lower internal thermal resistance and higher heat transfer rate from their cores to the package than that of standard electrolytic capacitors. U.S. Pat. No. 4,546,415 is hereby incorporated by reference into the present disclosure.
Various constructions of heat sinks, and techniques for improving their thermal efficiency, are known. Heat sinks made of aluminum, for example, are known in the art. Heat sinks are often finned to increase their surface area. The heat dissipating ability of a heat sink can be improved by using different length of finned stock or by the application of special coatings that are common in the heat sink industry, e.g., black anodizing. Another technique, for increasing the overall heat transfer rate from a heat sink, includes providing means of circulating a cooling fluid or gas through or around a heat sink.
Heat sinking can increase the dissipation of heat from the package of an electrolytic capacitor to the surrounding environment. Prior art attempts for dissipating the heat from the package have used radial type heat sinks surrounding the circumferential or peripheral surface of the package. Such arrangements, however, have not provided significant increase in thermal dissipation. Such arrangements also increase the "footprint" of the capacitors (i.e., the extent of the radial cross-sectional area of the capacitor), thus decreasing the available horizontal space in the equipment cabinet.
Other prior art devices have included a bolt at the insulated bottom of the capacitor package, to which a heat sink may be mounted. However, this arrangement has also not provided a significant increase in thermal dissipation.